Amplifier circuits



April17,1945. L, E. BARTON 2,374,071

.AMrLIFIER CIRCUIT Filed ngc. 19, '19:56

:L E *El Saune.: or Pawn? Patented Apr.'17, 1945 UNITED STATES PATENToFFlcs 2,374,071 s Y A Loy E. Barton, Collingswood, N. I., assignor, by

mesne assignments, to Philco Radio and Television Corporation,Philadelphia, Pa.,a` corporation of Delaware Application nmmber ,19.193s, sum No. naso: Great Britain August 4, 1936 19 Claims. `(Cl.179-171) This invention relates to improvements in radio amplifiercircuits and, morel particularly, to a novel degenerative combineddetector and audio amplifier system which may be used, for example, in aradio receiver, public address system, or the like, wherein it isdesired to amplify the audio frequency signals with a minimum ofdistortion.

The principal object of the invention is to provide an improved systemof this class embodying certain novel features or characteristics as setforth hereinafter in greater detail.

A more specific object of theinvention is to provide novel means forbiasing the detector in a system of this type which eliminates thenecessity of providing a relatively expensive filter condenser and, atthe same time, enables the minimizing of hum voltages introduced in thesignal channel through the detector plate circuit.

'Another object of the invention is to provide a novel tone control bymeans of which a selected portion of the audio frequency band may beaugmented or diminished by variation of the amount of degeneration orregeneration of the selected signal.

A further object of the invention is to provide novel means ,for varyingthe amount of degeneration of the lower frequencies, which variation maybe effected simultaneously with the volume adjustment, to thus vary therelative proportion ofvbass note reproduction.

Other objects and features of the system'will be apparent from thefollowing description and the accompanying drawing, the single figure ofwhich illustrates a combined detector and audio ampliiier system whichmay form part of a radio receiving system. It will be understood, ofcourse, that the invention is not limited tothe specific systemillustrated but is capable of use in any radio receiver or other systememploying an audio frequency amplifier and signal utilization means.Certain features of the invention may be employed, for example in asimple amplifier oircuit in which there is no detector or demodulator.

Referring to the drawing, there is shown a diodeftriode tube V1, thediode elements of which are adapted to function as a detector and may besupplied Vwith modulated carrier-wave sgnals by means of the tunedtransformer T1. .Such signals may be supplied from any suitable source,as represented by the source E. This signal source may, for example,represent the portion of a superheterodyne radio receiver preceding thesecond detector. Load resistors R1 and Rz are provided in the circuit ofthe diode rectifier and y quency signal to the control element or gridofI tube V1 which functions both as a detector and las an amplier aswell understood. It will be apparent that the signals appearing acrossthetapped portion ofthe potentiometer P1, plus any other signals whichmay be established between the cathode of tube V1 and ground, will besupplied to the control element of the tube.

The output of the tube V1 is obtained across the anode load resistor R3and is thence transferred by means of the coupling condenser C4 andresistor R4 to an amplifier tube V2, the output of'which is suppliedthrough an output transformer T2 to any suitable signal utilizationmeans such as the loud speaker LS. The tube V2 may be apentode asillustrated or any other'suitable power output tube and may, if desired,be

self-biased by means of the resistor Rs and associated condenser C5connected in the cathode lead of the tube as illustrated. The condenserCs shunted across the primary winding of the transformer T2 serves toby-passv signals of very high frequency and also serves to vary thephase of such signals to some degree.

A portion of the output signal from the secondary of transformer T2 maybe supplied through a coupling condenser C7 to a potentiometer Pscomprising two resistors R and Rn. The movable arm of the potentiometerP2 is adapted to move over both of the resistors Re and R1. grounded andthe cathode. of tube V1 may be connected tothe common point of resistorsRs and R7 as illustrated. The movable potentiometer arm is connectedthrough a condenser Cs to the cathode lead as illustrated for a purposewhich will be explained later. A condenser C9, whose purpose will alsobe explained later, is connected in shunt relation with the resistor Rn.

By means of this arrangement, a portion of the signal in the outputcircuit of the system may be returned to the input of the amplifiersystem in a manner to cause the amplifier system to be degenerative. Inother words, the potentiometer One end of the resistor R1 may be- P: isconnected to the transformer T2 in such a manner as to eil'ect feed-backof a signal which y serves to decrease the output signal of thesystern.l By virtue of the degenerative connection of the feed-backarrangement, any signal distortion incurred in the ampliiier channelwill be materially diminished.

It is to be noted further that this system effects simultaneousvariation of volume and degeneration in inverse relation to one anotherwhenever potentiometer P1 is actuated. In addition to the degenerativeor negative feed-back connection from potentiometer P2 to the cathode ofV1, there is a regenerative or positive feedback connection extendingfrom potentiometer P2 to the control grid of tube V1. This connectionextends through the resistor R2 and the coupling condenser C3 to theungrounded end of potentiometer P1. This positive feed-back pati issupplemented by a path in parallel with resistor R2, which includes thediode elements of tube V1, the secondary winding of transformer T1, andthe resistor R1. Whenever potentiometer 'P1 is actuated, the positivefeed-back voltage is varied in direct relation to the signal applied tothe grid of tube V1, and hence the over-all negative feed-back voltageis varied in inverse relation to the applied signal.

Considering the impedance relations involved, generally speaking, theloud speaker will have a very low impedance of the order of 1 or 2 ohms,while the potentiometer P2 may have an impedance of the order of 1000 or2000 ohms and, consequently, it will not cause any appreciable load onthe output circuit. On the other hand, the impedance associated with thetube V1 may be of the order of 100,000 ohms and, therefore, with respectto the tube V1, the resistor R1 may be considered to be a source ofsignals having substantially zero impedance.

Variations in the frequency response of the amplier system may beobtained by varying the amount of degeneration of signals oi thediii'erent frequencies and, in fact, under certain conditions, theampliiier system may be made regenerative in order to increase theresponse at certain frequencies. By suitably proportioning therespective circuit constants, this result may be obtained withoutaffecting the stability of the circuit. For example, the` condenser` C1will tend to reduce the amount of degeneration for those frequencies atwhich its impedance is comparable to the combined impedance of resistorsRe and R1. At such frequencies, the feed-back signal which is set upacross the resistor Rv is a relatively small proportion of the totalfeed-bacl-rA signal and, therefore, the amount of degeneration of thesystem is materially less than that obtaining for frequencies at whichthe impedance of condenser Cv is small or negligible in comparison tothe combined impedance of resistors Rs and Rv. It will be seen,therefore, that the condenser C1 may be utilized to provide basscompensation by designing this condenser so that it has an impedancecomparable to the impedance of potentiometer P2 for signals of thosefrequencies which sired to augment.

The condenser Ca may be utilized to decrease the high frequency responseof the amplifier systemwhen the potentiometer control arm is on theresistance Re. For normal signal feed-back, the potentiometer arm willbe positioned at the common point of the two resistors Re and R1 and,therefore. when the potentiometer'arm is on the it 1S deresistance Re,the signal feed-back will be greater than normal. 0n the other hand,when the potentiometer arm is on the resistance Rv, the sig' nalfeed-back will be less than normal.

The resistance R1 will be small in comparison to the other resistors ofthe circuit of tube V1 and, therefore. no degeneration will occur in thetube V1 and its associated circuits other than the degenerative actionof the system as whole. Therefore, maximum gain is obtained from theamplifier portion of the tube V1. .In order to provide adequate bias forthe control element of tube V1, however, there is provided a resistanceRs which is connected between .the high potential side oi the powersupply circuit and the resistor Rn. In this manner, a unidirectionalcurrent is caused to flow through resistor R1 which sets up aunidirectional voltage across this resistor, providing a suitable biasfor the. control element of tube V1. This arrangement serves anadditional important function in that it enables complete balancing outor bucking of hum signals. By connecting the resistor Ra to a suitablepoint on the power supply unit as illustrated and by properly designingthe several circuit constants, complete hum bucking action may beobtained. It will be seen that the ripple voltage inthe power supplyunit, which is inherently present due to the filtering action of thefilter, is applied to the grid circuit of tube V1 through resistors Reand Rv and is also applied to the plate of tube V1 through resistors Reand R3. Moreover, it will be apparent that the phase of the signalsapplied to these two elements of tube V1 will be the same. Due to thephase reversal which takes place in the tube V1, the hum signal suppliedto the grid circuit of the tube may be made to balance or buck out thehum signal supplied to the plate circuit of the tube. 'I'his actionobtains when the ratio of the hum signal across resistor R1 to the humsignal built up across resistor R4 is equal to the amplification or gainof the tube V1 and when the two signals are alike in phase. The phaserelation of these two signals may be controlled by proper design oi thevalues of Rs, Rv, Re and Rio and the condensers Cs and Cm. By suitabledesign of these circuit constants, substantially complete humelimination may be obtained.

It may now be noted that the condenser Ca may be a relatively smallcondenser which serves to control the phase of the hum signal acrossresistor Rv rather than to prevent the formation of a hum signal acrossthis resistor. This condenser replaces a relatively large and costlyfilter condenser which has been used in self-biasing arrangements. Inthis respect, the present invention effects an economy which isimportant in present day mass production.

The power supply unit may comprise a transformer Ta, a rectifier Va anda conventional filter including shunt condensers C11 and C12 and aseries choke coil L. The. resistor Rm may be used to supply other tubesof the system.

In a specific system by means of which the results set forth above wereobtained, the following circuit constants were employed:

Ri 50.000 ohms R 330,000 ohms R 1=250,000 ohms R4 1 megohm R6 1,400 ohmsR7 600 ohms R8: 190,000 ohms B9=3,300 ohms 1- .0 me ohms Rw=75,000 ohmsEpl-245 vo ts Eg-210 volts asesora The tube V1 may be a '15 typedicde-triode tube. while the tube V2 may be a SFS type tube. The powersupply unit may be adapted to operate from a 60 cycle A. C. source.

Fromthe above description and the accompanying illustration, it will beseen that the invention providesa novel degenerative circuit by a verymw level and variation in frequency respense may be obtained by varyingthe amount of degeneration. Moreover, the invention provides novel meansfor obtaining both base compensation and high frequency compensation.While either of these may be fixed orv variable, the arrangementillustrated enabling variation of the high frequency compensation isparticularly desirable.v The invention provides further a simple andconvenient method of eliminating hum while, at the same time, providinga suitable bias for the input tube of the regenerative system.

llt will be understood, of course, that the invention is not limited tothe specific system illustrated but is capable of various changes andmodifications without departing from its scope.

I claim: 'i

l. In a signal amplifying device having an input circuit and an outputcircuit, said device including a space discharge device having grid andcathode electrodes connected to said input circuit, a potentiometer, amanually adjustable contact on said potentiometer, means connecting saidpotentiometer in shunt with said output circuit, a fixed intermediatetap on said potentiometer, means connecting one of said electrodes tosaid fixed intermediate tap whereby a portion of said potentiometer isincluded in said input circuit, and a connection including a reactancebetween said fixed tapand said adjustable contact, whereby the frequencyresponse of said device may be varied by positioning said adjustablecontact in relation to said fixed tap.

2. In a signal amplifying device having an input circuit and an outputcircuit, said deviceV including a space discharge device having a gridand a cathode connected to said'input circuit, a potentiometer, amanually adjustable contact on said potentiometer, means connecting saidpotentiometer in shunt with said output circuit, a fixed intermediatetap on said potentiometer, means connecting said cathode to said fixedintermediate tap whereby a portion of said potentiometer is included insaid input circuit, and a v connection including a reactance betweensaid fixed tap and said adjustable contact, whereby the 'frequencyresponse of said device may be varied by positioning said adjustablecontact in relation to said fixed tap.

3. In' a signal amplifying device having an input circuit and an outputcircuit, said device including'a .space discharge device having a gridand a cathode, connected to said input circuit, a potentiometer, amanually adjustable contact on said potentiometer, means including acondenser connecting said potentiometer in shunt with said outputcircuit, a fixed intermediate tap on said potentiometer, meansconnecting said cathode to said xed intermediate tap whereby a portionof said potentiometer is serially included in said input circuit, and aconnection including a second condenser between said fixed tap and saidadjustable contact.

4. In a signal amplifying device having .an inputcircuit and an outputcircuit, said device inf f cluding a space discharge device having a.grid

and a cathode connected to said input circuit, a

- means' of which signal distortion, may be kept at saidpotentiometenmeans including a condenser connecting said potentiometerinshunt with said output circuit, a fixed intermediate tap on saidpotentiometer, means connecting said cathode to said xedintermediate tapwhereby a portion of :said potentiometer is serially included in saidinsaid potentiometer, means including a condenser connecting saidpotentiometer in shunt with said output circuit, a fined intermediatetap on said potentiometer, means connecting said cathode to said xedintermediate tap whereby a portion of' said potentiometer is seriallyincluded in said input circuit, and a connection including a secondcondenser between'said fixed tap and said adjustable contact, saidfirst-mentioned condenser having a reactance which is comparable to theresistance of said potentiometer at a predetermined low audio frequency,whereby there results a decrease in degeneration below saidpredetermined frequency.

6. In an audio frequency amplifier having an input circuit and an outputcircuit, said amplifier including a space discharge device having a gridand a cathode connected to said input circuit, a potentiometer, amanually adjustable contact on said potentiometer, means including acondenser connecting said potentiometer in shunt with lsaid outputcircuit, a fixed intermediate tap on said potentiometer, meansconnecting said cathode to said fixed intermediate tap whereby a portionof said potentiometer is serially included in said input circuit, and 'aconnection including a second condenser between said fixed tap and saidadjustable contact, the reactancve of said second condenser being sorelated to the reactance of the first-mentioned condenser and theresistance of said potentiometer, that the degeneration of high audiofrequencies increases as said adjustablel contact is moved toward, saidfirst-mentioned condenser. 1

7. In a signal amplifying device having an in- Put circuit and an outputcircuit, said device including a, space discharge device having grid andcathode electrodes connected to said input circuit, a potentiometer, a.manually adjustable contact on said potentiometer, means connecting saidpotentiometer in shunt with said output circuit, a fixed intermediatetap on said poten' tiometer, said intermediate tap lyingv between theouter limits of movementy of saidiadjustable Contact, means connectingone `of said electrodes to said i'lxed intermediate tap whereby aportion of said potentiometer is includedin said input circuit, and aconnection including a'freactance between said xed tap and saidadjustable contact, whereby Vthe frequency response of said device maybe varied by positioning said adjustable contact in relation to saidfixed tap.

8. In a. signal amplifying device having an input circuit and an outputcircuit, said device including a, space discharge device having a gridand a cathode connected to said input circuit,

a potentiometer, a. manually adjustable contact potentiometer, amanually adjustable contact "on denser connecting said potentiometer inshunt with said output circuit, a nxed intermediate tap on saidpotentiometer, said intermediate tap lying between the outer limits ofmovement of said adjustable contact, means connecting said cathode tosaid fixed intermediate tap whereby a portion of said potentiometer isserially included in said input circuit, a connection including a secondcondenser between said fixed tap and said adjustable contact, and athird condenser connected between said fixed tap and one side of saidoutput circuit.

9. In an audio frequency amplifier having an input circuit and an outputcircuit, said ampliner including a space discharge device having a gridand a cathode connected'to said input circuit, a potentiometer, amanually adjustable contact on said potentiometer, means including acondenser connecting said potentiometer in shunt with said outputcircuit, s, fixed intermediate tap on said potentiometer, saidintermediate tap lying between the outer limits of movement of saidadjustable contact, means connecting said cathode to said fixedintermediate tap whereby a portion of said potentiometer is seriallyincluded in said input circuit, and a connection including a secondcondenser between said iixed tap and said adjustable contact, thereactance of said second condenser `being so related to the reactance ofthe first-mentioned condenser and the resistance of said potentiometer,that the degeneration of high audio frequencies increases as saidadjustable contact is moved toward said mst-mentioned condenser.

10. In an audio amplifying system, an audio channel including at leastone space discharge device having an input circuit, means for supplyingan input signal to said input circuit, a degenerative connection fromsaid audio channel to said input circuit for supplying a degenerativecontrol signal to the input circuit, and means for simultaneouslyvarying the amplitude of the input signal and the amplitude of thedegenerative control signal in inverse relation to one another.

l1. An audio frequency amplier system comprising an electron dischargeamplifier .having an anode, a cathode and agrid, means for sup- Plying asignal to be amplified, a potentiometer connected in circuit with saidsignal supplying means and having its arm connected with said grid, aresistor connected between the low potential'end of said potentiometerand said cathode, and means connected across said resistor for supplyingthereto a feed back voltage controlled by the current in theanode-cathode circuit.

l2, In an audio signal voltage transmission system, a source of audiosignal voltage, an audio amplier having input and output circuits,means'for controlling the magnitude of the said voltage impressed onsaid input circuit, an audio signal voltage feed back circuit betweenthe amplifier output circuit and input circuit for .feeding back signalVoltage in degenerative phase, and a second feed back circuit forfeeding back signal voltage in regenerative phase, said controllingmeans being included in one of said feed back circuits therebysimultaneously to control the magnitude of one of said feed back volt-8898.

13. In an audio amplifying system, an audio amplifier having an inputcircuit and an output circuit, an audio channel connected to said outputcircuit, a gain control potentiometer connected in said input circuit tovary the input signal applied thereto, and a degenerative connectionfrom said audio channel to a predetermined intermediate tap point onsaid potentiometer for supplying to said input circuit a degenerativecontrol signal whose amplitude varies in inverse -relation to theamplitude of the input signal over a potentiometer and a resistorconnected to be` traversed in series by the signal to be amplified,means connecting said resistor and the adjacent adjustable portion ofsaid potentiometer in said input circuit, and means for applying acrosssaid` resistor a feedback voltage in accordance with the current in saidoutput circuit.

15. An audio frequency amplifier system comprising an electron dischargeampliiier having an input circuit and an output circuit, means forsupplying a signal voltage to be amplified, means separate from andcontrolled -by said output circuit for producing a feedback voltage, anda device connected with said signal voltage supplying means, with saidfeedback voltage producing means and with said input circuit forsimultaneously increasing the proportion of signal voltage applied tothe input circuit and decreasing the proportion of feedback voltagesupplied thereto, and said feedbackl voltage means being constructed tohave a frequency discriminating characteristic.

16. An audio frequency amplifier system comprising an electron dischargeamplifier having an input circuit and an outputl circuit, means forsupplying a signal voltage to be amplified, means separate from andcontrolled by said output circuit for producing a feed-back voltage, anda device connected with said signal voltage supplying means, with saidfeed-back voltage producing means and with said input circuit forsimultaneously increasing the proportion of signal voltage applied tothe input circuit and decreasing the proportion of feed-back voltagesupplied thereto. 17. An audio frequency amplifier system comprising anelectron discharge amplifier having an input circuit and an outputcircuit, the resistance of the output circuit lbeing fixed, means forsupplying a signal voltage to be amplified, means for supplying afeed-back voltage controlled by the current in said output circuit, anda device connected with said signal voltage supplying means, with saidfeed-back voltage supplying means and with said input circuit forsimultaneously increasing the proportion of signal voltage applied tothe input circuit and decreasing the proportion of feed-back voltagesupplied thereto.

18. In" a radio receiver, a'souce of audio signals, an audio amplifierhaving an input circuit and an output circuit, a volume control deviceconnected to said source and connecting said input circuit to saidoutput circuit degeneratively for transferring to said input circuitcontrollable portions of the signal in said output circuit and, thesignal from said source, said degeneratively connected volume controldevice including means for varying the said portions of said signals insuch manner that the degenerative signal increases from a relatively lowvalue to a maximum value as the volume control is progressively adjustedto decrease the output level from a maximum value to a low value.-

19. In an audio amplifying system, an audio ing said voltageregeneratively to said potentiom` eter, and means tor deriving anothervoltage from said output circuit and for applying said Ivoltagedegenerativeiy to said input circuit, to thereby apply to said inputcircuit a resultant degenerative voltage whose magnitude variesinversely LOY E. BARTON.

lvffith the magnitude o! the input signal.

